Firefighters were called to Swift Transportation in the 11800 block of Mission Boulevard about 7:45 p.m. Friday, to respond to a report of employees being ``overcome by an odor of unknown substance in a trailer,'' county fire department spokeswoman Melody Hendrickson said.

Initially, there were 29 employees taken to hospitals, Hendrickson said.

By 10:35 p.m. Friday night, another six employees reported feeling sick, bringing the total taken to hospitals to 35.

Forty firefighters from 10 engine companies, along with a hazardous materials team, responded to the scene, Hendrickson said.

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